Hitherto, many diacylperoxides have been synthesized and studied, and various diacylperoxides useful as initiators in the polymer industries are prepared and commercially available.
The peroxide to be used as a polymerization initiator for a fluorine-containing monomer is generally required to have following characteristics:
1. Since the fluorine-containing monomer usually has high reactivity, it is desirable to carry out their polymerization under milder condition, for example, at a low temperature. Accordingly, the peroxide is required to liberate an active radical at a low temperature.
2. Since radicals of propagating fluorine-containing polymeric chains generated during polymerization are active, the peroxide desirably hardly proceeds or does not proceed side reactions such as chain transfer reaction.
3. Peroxide residues bonded to the chain ends of the polymer molecules should be thermally stable.
As the peroxides which satisfy the above requirements, there are fluorine-containing diacylperoxides such as EQU [Cl(CF.sub.2 CFCl).sub.n CF.sub.2 COO--.sub.2 (DLP) EQU [H(CF.sub.2 CF.sub.2).sub.n COO--.sub.2 (DHP) EQU [ClCF.sub.2 CF.sub.2 COO--.sub.2 (DIP) EQU [CF.sub.3 CF.sub.2 COO--.sub.2 (3P).
However, these conventional fluorine-containing diacylperoxides are used at a polymerization temperature of 10.degree. to 40.degree. C. or higher to achieve a practical decomposition rate of the peroxide.